1. Field of the Invention
The present invention relates to a charge-coupled array (CCD) having a multi-layer structure for imaging full-color images.
2. Description of the Prior Art
Charge-coupled arrays (CCD's) are generally defined as layered structures for the selective retention of charge in specific areas thereof, wherein the structure itself may serve as a shift register for selective serial readout of data in the form of the charged areas. Discrete areas within the CCD are caused to store charge because the electrical potential is lower in the particular area holding the charge than in the surrounding material. When it is desired to read out the charges as a serial signal, the charge in each area can be transferred from one area to its neighbor by suitably changing the potential on it and its neighbors so that charge flows from one area to the next. By applying charges to a linear series of electrodes along the array, typically with some time period of overlap of charging adjacent electrodes, individual charge packets can be caused to move along the CCD. The system for transferring discrete charges from one area to the next until the charges are read out as a serial signal is colloquially known as the "bucket-brigade" method of readout. An early patent describing the shift register operation of a CCD is U.S. Pat. No. 3,758,794.
One special type of CCD is the photosensitive, or "imaging," CCD, wherein discrete areas of charge, which may be read out as serial signals, are initially created in the CCD by the imagewise focusing of light onto the structure. With certain materials, such as aluminum, gallium, and arsenic compounds and combinations in an ordered crystal structure, photons focused on the material will create electron-hole pairs in areas corresponding to the distribution of light in the image. Thus, the CCD forms a linear array of photosensors upon which narrow sections of an image can be recorded, while the CCD can output data related to the image. Such CCD's, particularly monochrome CCD's, are in common use in facsimile machines, digital copiers, and other scanners. Typical examples of such an imaging CCD are shown in U.S. Pat. Nos. 3,971,003; 4,658,278; and 4,667,213.
U.S. Pat. No. 4,383,269 discloses a photodetector (as opposed to a CCD) having an energy band structure which causes one type of charge carrier, either an electron or a proton, to ionize at a faster rate than the other type of charge carrier. The photodetector is preferably formed from semiconductors including gallium, aluminum, arsenic, and phosphides.
U.S. Pat. No. 4,432,017 discloses a high density imaging CCD having a bilinear array of photosites on a single integrated circuit chip. The photosites are offset relative to each other in two rows and coupled to a respective pair of storage registers and shift registers.
U.S. Pat. No. 4,613,895 discloses a solid state color imaging device having a plurality of regions of alternating dopant types within the material thereof. A first channel collects a first photosignal in a first region extending to a first depth of the element, and a buried channel disposed beneath the first channel collects a second photosignal in a second region extending to a depth greater than the first step. Light falling on the surface of the device penetrates the device to a wavelength-dependent depth. The color response of various portions of the device are dependent on the type and thickness of different layers of the device.
U.S. Pat. No. 4,847,489 discloses a superlattice photodetector arrangement having a plurality of photosensitive detector elements, each element having a multi-layer structure of alternating positively and negatively doped photosensitive semiconductor material. Control electrodes are arranged vertically with respect to the semiconductor layers, and adapted to receive a control voltage in order to control the spectral light sensitivity thereof.
U.S. Pat. No. 4,975,567 discloses a photodetector with a multi-layer structure, wherein different layers of the structure are sensitive to different wavelength bands, and the different layers differing by thickness. Pairs of electrical contacts are applied to each relevant semiconductor layer, and are adapted to receive associated bias voltages to enable the photosensitive layers to constitute a plurality of separate photodetectors, each having a different wavelength band.
U.S. Pat. No. 5,138,416 discloses a multi-layer color photosensitive element having different layers, each sensitive to a different primary color, and differing primarily by composition. Charge is collected from the various layers according to an amount of time for light of various colors to travel through the layers.
IBM Technical Disclosure Bulletin, Vol. 12, no. 9, page 1486, discloses a photo device having the ability to discriminate light of different wavelengths, and converting these different energies into separable electrical signals. Alternating layers of the structure either optically absorb light of a given wavelength, or lack sufficient band gap for other wavelengths, and an arrangement of these layers allows the multi-layer structure to discriminate.
The paper "Improved Two Wavelength Demultiplexing InGaAsP Photodetector" discloses various stacked layer structures to integrate both detection and demultiplexing functions in a single photodetector.